U.S. patent number 7,647,155 [Application Number 11/663,811] was granted by the patent office on 2010-01-12 for apparatus and method for calculating work load engine.
This patent grant is currently assigned to Honda Motor Co., Ltd.. Invention is credited to Koichi Ikoma, Katsura Okubo, Masahiro Sato, Koichiro Shinozaki, Yuji Yasui.
United States Patent |
7,647,155 |
Shinozaki , et al. |
January 12, 2010 |
Apparatus and method for calculating work load engine
Abstract
A device and method for calculating the work load of an engine
more efficiently and accurately. The device for calculating the
work load of an engine comprises a means for determining a desired
frequency component to calculate the work load of the engine
obtained through frequency decomposition of the volume variation
rate of the engine. The device further comprises a first
calculating means for calculating a first correlation coefficient
between the volume variation rate and a reference signal composed
of a frequency corresponding to the determined component, and a
second calculating means for calculating a second correlation
coefficient between the cylinder inner pressure of the engine and a
reference signal composed of a frequency corresponding to the
determined component. The work load of the engine is calculated
using the first and second correlation coefficients.
Inventors: |
Shinozaki; Koichiro (Saitama,
JP), Okubo; Katsura (Saitama, JP), Yasui;
Yuji (Saitama, JP), Sato; Masahiro (Saitama,
JP), Ikoma; Koichi (Saitama, JP) |
Assignee: |
Honda Motor Co., Ltd. (Tokyo,
JP)
|
Family
ID: |
36118988 |
Appl.
No.: |
11/663,811 |
Filed: |
September 28, 2005 |
PCT
Filed: |
September 28, 2005 |
PCT No.: |
PCT/JP2005/017894 |
371(c)(1),(2),(4) Date: |
February 19, 2008 |
PCT
Pub. No.: |
WO2006/035842 |
PCT
Pub. Date: |
April 06, 2006 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20080294323 A1 |
Nov 27, 2008 |
|
Foreign Application Priority Data
|
|
|
|
|
Sep 30, 2004 [JP] |
|
|
2004-287982 |
|
Current U.S.
Class: |
701/102 |
Current CPC
Class: |
G01L
23/225 (20130101); G01L 5/0095 (20130101); F02D
35/023 (20130101); F02D 15/02 (20130101); F02D
2041/288 (20130101); F02D 2250/12 (20130101); F02D
2200/1004 (20130101) |
Current International
Class: |
F02D
45/00 (20060101); F02D 15/02 (20060101); G01M
15/00 (20060101) |
Field of
Search: |
;701/102,101,115 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
3-057937 |
|
Mar 1991 |
|
JP |
|
7-034958 |
|
Feb 1995 |
|
JP |
|
Primary Examiner: Vo; Hieu T
Attorney, Agent or Firm: Arent Fox LLP
Claims
The invention claimed is:
1. An apparatus for calculating work of an engine, the apparatus
comprising: desired component determining means for determining a
frequency component desired for calculating the engine work, among
frequency components obtained by frequency-resolving a volume
change rate of the engine; first determination means for
determining a first correlation coefficient between the volume
change rate and a reference signal that consists of the desired
frequency component; second determination means for determining a
second correlation coefficient between an in-cylinder pressure of
the engine and a reference signal that consists of the desired
frequency component; and engine work calculating means for
calculating the engine work based on the first correlation
coefficient and the second correlation coefficient.
2. The apparatus of claim 1, wherein the first correlation
coefficient is a Fourier coefficient that is obtained by expanding
the volume change rate into Fourier series and the second
correlation coefficient is a Fourier coefficient that is obtained
by expanding the in-cylinder pressure into Fourier series.
3. The apparatus of claim 1, further comprising: a mechanism for
changing a stroke volume of the engine; and stroke volume
determining means for determining the stroke volume, wherein the
engine work calculating means calculates the engine work based on
the determined stroke volume, the first correlation coefficient and
the second correlation coefficient.
4. The apparatus of claim 3, further comprising: storage means for
storing a stroke volume that is predetermined corresponding to an
operating condition of the engine; and means for detecting an
operating condition of the engine, wherein the stroke volume
determining means refers to the storage means based on the detected
operating condition of the engine to extract the stroke volume
corresponding to the detected operating condition.
5. The apparatus of claim 1, further comprising means for detecting
an operating condition of the engine, wherein the desired component
determining means determines the desired frequency component based
on the detected operating condition of the engine.
6. The apparatus of claim 5, wherein the engine includes a
mechanism that is capable of changing a compression ratio of the
engine; and wherein the operating condition of the engine includes
the compression ratio of the engine.
7. The apparatus of claim 1, further comprising: storage means for
storing a desired component and a first correlation coefficient
that are predetermined corresponding to an operating condition of
the engine; and means for detecting an operating condition of the
engine, wherein the desired component determining means refers to
the storage means based on the detected operating condition of the
engine to extract the desired component corresponding to the
detected operating condition; and wherein the first determination
means refers to the storage means based on the detected operating
condition of the engine to extract the first correlation
coefficient corresponding to the detected operating condition.
8. The apparatus of claim 1, further comprising means for detecting
an in-cylinder pressure of the engine, wherein the second
determination means calculates the second correlation coefficient
based on the detected in-cylinder pressure in accordance with a
predetermined equation.
9. The apparatus of claim 1, further comprising: storage means for
storing, for the desired components and the first correlation
coefficient corresponding to the desired component, a first
component in a first operating condition of the engine and a first
correlation coefficient corresponding to the first component and a
second component in a second operating condition of the engine and
a first correlation coefficient corresponding to the second
component; and means for detecting an operating condition of the
engine, wherein if the engine operating condition detected by the
means for detecting an operating condition of the engine is between
the first condition and the second condition, the first
determination means determines the first correlation coefficient
corresponding to the detected operating condition of the engine by
interpolating between the first correlation coefficient
corresponding to the first component and the first correlation
coefficient corresponding to the second component.
10. The apparatus of claim 9, further comprising: storage means for
storing, for a stroke volume of the engine, a first stroke volume
in the first operating condition of the engine and a second stroke
volume in the second operating condition of the engine; and means
for determining a stroke volume corresponding to the detected
operating condition of the engine by interpolating between the
first stroke volume and the second stroke volume if the engine
operating condition detected by the means for detecting an
operating condition of the engine is between the first condition
and the second condition, wherein the engine work calculating means
calculates the engine work based on the determined stroke volume,
the first correlation coefficient and the second correlation
coefficient.
11. The apparatus of claim 1, further comprising means for
detecting an operating condition of the engine, wherein the first
determination means determines the volume change rate corresponding
to the detected operating condition of the engine and calculates
the first correlation coefficient based on the determined volume
change rate in accordance with a predetermined equation.
12. The apparatus of claim 1, wherein the engine work comprises an
indicated mean effective pressure.
13. An apparatus for calculating work of an engine, the apparatus
comprising a control unit configured to: determine a frequency
component desired for calculating the engine work, among frequency
components obtained by frequency-resolving a volume change rate of
the engine; determine a first correlation coefficient between the
volume change rate and a reference signal that consists of the
desired frequency component; determine a second correlation
coefficient between an in-cylinder pressure of the engine and a
reference signal that consists of the desired frequency component;
and calculate the engine work based on the first correlation
coefficient and the second correlation coefficient.
14. The apparatus of claim 13, wherein the first correlation
coefficient is a Fourier coefficient that is obtained by expanding
the volume change rate into Fourier series and the second
correlation coefficient is a Fourier coefficient that is obtained
by expanding the in-cylinder pressure into Fourier series.
15. The apparatus of claim 13, further comprising a mechanism for
changing a stroke volume of the engine; and wherein the control
unit is further configured to: determine the stroke volume; and
calculate the engine work based on the determined stroke volume,
the first correlation coefficient and the second correlation
coefficient.
16. The apparatus of claim 15, wherein the control unit comprises a
storage unit for storing a stroke volume that is predetermined
corresponding to an operating condition of the engine; and wherein
the control unit is further configured to: detect an operating
condition of the engine; and refer to the storage unit based on the
detected operating condition of the engine to extract the stroke
volume corresponding to the detected operating condition.
17. The apparatus of claim 13, wherein the control unit is further
configured to: detect an operating condition of the engine; and
determine the desired frequency component based on the detected
operating condition of the engine.
18. The apparatus of claim 17, wherein the engine includes a
mechanism that is capable of changing a compression ratio of the
engine; and wherein the operating condition of the engine includes
the compression ratio of the engine.
19. The apparatus of claim 13, wherein the control unit comprises a
storage unit for storing a desired component and a first
correlation coefficient that are predetermined corresponding to an
operating condition of the engine; and wherein the control unit is
further configured to: detect an operating condition of the engine;
refer to the storage unit based on the detected operating condition
of the engine to extract the desired component corresponding to the
detected operating condition and refer to the storage unit based on
the detected operating condition of the engine to extract the first
correlation coefficient corresponding to the detected operating
condition.
20. The apparatus of claim 13, further comprising a unit for
detecting an in-cylinder pressure of the engine, wherein the
control unit is further configured to calculate the second
correlation coefficient based on the detected in-cylinder pressure
in accordance with a predetermined equation.
21. The apparatus of claim 13, further comprising: a storage unit
for storing, for the desired components and the first correlation
coefficient corresponding to the desired component, a first
component in a first operating condition of the engine and a first
correlation coefficient corresponding to the first component and a
second component in a second operating condition of the engine and
a first correlation coefficient corresponding to the second
component; and wherein the control unit is further configured to:
detect an operating condition of the engine; and if the engine
operating condition thus detected is between the first condition
and the second condition, determine the first correlation
coefficient corresponding to the detected operating condition of
the engine by interpolating between the first correlation
coefficient corresponding to the first component and the first
correlation coefficient corresponding to the second component.
22. The apparatus of claim 21, further comprising: a storage unit
for storing, for a stroke volume of the engine, a first stroke
volume in the first operating condition of the engine and a second
stroke volume in the second operating condition of the engine; and
wherein the control unit is further configured to: determine a
stroke volume corresponding to the detected operating condition of
the engine by interpolating between the first stroke volume and the
second stroke volume if the detected engine operating condition is
between the first condition and the second condition; and calculate
the engine work based on the determined stroke volume, the first
correlation coefficient and the second correlation coefficient.
23. The apparatus of claim 13, wherein the control unit is further
configured to: detect an operating condition of the engine;
determine the volume change rate corresponding to the detected
operating condition of the engine; and calculate the first
correlation coefficient based on the determined volume change rate
in accordance with a predetermined equation.
24. The apparatus of claim 13, wherein the engine work comprises an
indicated mean effective pressure.
25. A method for calculating work of an engine, comprising: (a)
determining a frequency component desired for calculating the
engine work, among frequency components obtained by
frequency-resolving a volume change rate of the engine; (b)
determining a first correlation coefficient between the volume
change rate and a reference signal consisting of the desired
frequency component; (c) determining a second correlation
coefficient between an in-cylinder pressure of the engine and a
reference signal consisting of the desired frequency component; and
(d) calculating the engine work based on the first correlation
coefficient and the second correlation coefficient.
26. The method of claim 25, wherein the first correlation
coefficient is a Fourier coefficient obtained by expanding the
volume change rate into Fourier series and the second correlation
coefficient is a Fourier coefficient obtained by expanding the
in-cylinder pressure into Fourier series.
27. The method of claim 25, further comprising determining a stroke
volume of the engine, wherein the step (d) further includes
calculating the engine work based on the stroke volume, the first
correlation coefficient and the second correlation coefficient.
28. The method of claim 27, further comprising: providing a storage
device for storing a stroke volume predetermined corresponding to
an operating condition of the engine; and detecting an operating
condition of the engine, wherein said step for determining a stroke
volume includes referring to the storage device based on the
detected operating condition of the engine to extract the stroke
volume corresponding to the detected operating condition of the
engine.
29. The method of claim 25, further comprising detecting an
operating condition of the engine, wherein the step (a) includes
determining the desired component based on the detected operating
condition of the engine.
30. The method of claim 29, wherein the engine includes a mechanism
that is capable of changing a compression ratio of the engine; and
wherein the operating condition of the engine includes the
compression ratio of the engine.
31. The method of claim 25, further comprising: providing a storage
device for storing the desired component and the first correlation
coefficient that are predetermined corresponding to an operating
condition of the engine; and detecting an operating condition of
the engine, wherein the step (a) includes referring to the storage
device based on the detected operating condition of the engine to
extract the desired component corresponding to the detected
operating condition of the engine; and wherein said step (b)
includes referring to the storage device based on the detected
operating condition of the engine to extract the first correlation
coefficient corresponding to the detected operating condition of
the engine.
32. The method of claim 25, further comprising detecting an
in-cylinder pressure of the engine, wherein the step (c) includes
calculating the second correlation coefficient based on the
detected in-cylinder pressure in accordance with a predetermined
equation.
33. The method of claim 25, further comprising: providing a storage
device for storing, for the desired component and the first
correlation coefficient corresponding to the desired component, a
first component in a first operating condition of the engine and a
first correlation coefficient corresponding to the first component,
and a second component in a second operating condition of the
engine and a first correlation coefficient corresponding to the
second component; and detecting an operating condition of the
engine, wherein if the detected operating condition is between the
first operating condition and the second operating condition, the
step (b) determines the first correlation coefficient corresponding
to the detected operating condition of the engine by interpolating
between the first correlation coefficient corresponding to the
first component and the first correlation coefficient corresponding
to the second component.
34. The method of claim 33, further comprising: providing a storage
device for storing, for a stroke volume of the engine, a first
stroke volume in the first operating condition of the engine and a
second stroke volume in the second operating condition of the
engine; and determining a stroke volume corresponding to the
detected operating condition of the engine by interpolating between
the first stroke volume and the second stroke volume if the
detected engine operating condition is between the first condition
and the second condition, wherein the step (d) calculates the
engine work based on the determined stroke volume, the first
correlation coefficient and the second correlation coefficient.
35. The method of claim 25, further comprising detecting an
operating condition of the engine, wherein said step (b) includes
determining the volume change rate corresponding to the detected
operating condition of the engine and calculating the first
correlation coefficient based on the determined volume change rate
in accordance with a predetermined equation.
36. The method of claim 25, wherein the engine work includes an
indicated mean effective pressure.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application is a National Stage entry of International
Application No. PCT/JP2005107894, filed Sep. 28, 2005, the entire
specification claims and drawings of which are incorporated
herewith by reference.
TECHNICAL FIELD
The present invention relates to an apparatus and a method for
efficiently calculating work performed by an internal-combustion
engine.
BACKGROUND ART
Some techniques have been proposed for detecting a pressure within
a combustion chamber (referred to as an in-cylinder pressure) of a
internal-combustion engine (referred to as an engine) to calculate
engine work such as an indicated mean effective pressure based on
the detected pressure and a rate of change in the stroke volume of
the combustion chamber.
Japanese Patent Application Publication listed below discloses a
technique for deriving an equation to be used for calculating an
indicated mean effective pressure for an engine having a
predetermined structure. This equation uses predetermined frequency
components of an in-cylinder pressure signal. In order to extract
the predetermined frequency components of the in-cylinder pressure
signal, the in-cylinder pressure signal is filtered by a first
band-pass filter for extracting a fundamental wave component and a
second band-pass filter for extracting higher harmonic wave
components that are integral multiples of the fundamental wave
component.
Patent application publication 1: No. H8-20339
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
Conventionally, in order to calculate engine work such as an
indicated mean effective pressure, it is required that the
in-cylinder pressure is sampled at a higher frequency (for example,
at every one degree crank angle). Such a higher sampling frequency
makes the calculation load higher, which may be difficult for
calculation performed by a control unit (ECU) mounted on a
vehicle.
The technique disclosed in the above patent application publication
attempts to lower the sampling frequency. More specifically,
according to this technique, frequency components required for
calculating the indicated mean effective pressure are
predetermined. The sampling frequency can be decreased to the point
where the predetermined frequency components can be obtained.
However, according to this technique, the predetermined frequency
components are extracted by using a band-pass filter. It may be
difficult for the band-pass filter to accurately extract the
predetermined frequency components. If the accuracy of the
filtering is improved, the band-pass filter may become unstable. As
a result, an error in the filtered in-cylinder pressure signal may
be larger.
Further, according to the technique disclosed in the above patent
application publication, the equation used for calculating the
indicated mean effective pressure is derived assuming that the
engine has a predetermined structure. Therefore, it is difficult to
apply such an equation to another engine having a structure
different from the predetermined structure.
Further, according to the technique disclosed in the above patent
application publication, the in-cylinder pressure needs to be
sampled at a predetermined angle with respect to the top dead
center (TDC) of the intake stroke. Therefore, a time period over
which the indicated mean effective pressure is calculated is fixed,
cannot be arbitrarily established. On the other hand, in a typical
engine, a stroke volume is constant. Therefore, the waveform of a
rate of change in the stroke volume (referred to as volume change
rate hereinafter) with respect to the crank angle of the engine is
constant. Accordingly, engine work such as the indicated mean
effective pressure has been conventionally calculated assuming that
the waveform of the volume change rate is constant.
In recent years, however, there is proposed an engine where the
stroke volume is variable and hence the waveform of the volume
change rate with respect to the crank angle of the engine is
variable. For example, in an engine with a variable compression
ratio mechanism, the stroke volume and the volume change rate can
change. When engine work is calculated for such an engine according
to the conventional technique, various stroke volumes and volume
change rates corresponding to various engine operating conditions
need to be pre-stored in a memory, which is enormous amount of
data.
Moreover, according to the technique disclosed in the above patent
application publication, the equation for calculating the indicated
mean effective pressure is derived assuming that the volume change
rate is expressed by a predetermined single equation. Because the
derived equation does not include any parameter regarding the
volume change rate, accurate calculation of the indicated mean
effective pressure is difficult for an engine where the waveform of
the volume change rate is variable.
Thus, an object of the present invention is to provide an apparatus
and a method for calculating engine work in such a manner as to
solve the above-described problems.
Means for Solving Problem
According to one aspect of the present invention, a method for
calculating work of an engine comprises determining a component
desired for determining the engine work, among frequency components
that are obtained by frequency-resolving a volume change rate of
the engine. The method further comprises determining a first
correlation coefficient between the volume change rate and a
reference signal that consists of a frequency corresponding to the
desired component and a second correlation coefficient between an
in-cylinder pressure of the engine and a reference signal that
consists of a frequency corresponding to the desired component. The
engine work is calculated based on the first and second correlation
coefficients.
According to the invention, the second correlation coefficient
associated with the in-cylinder pressure is calculated only for the
desired component that is determined by frequency-resolving the
volume change rate. All of the components are not required for
calculating the second correlation coefficient. Consequently, the
sampling frequency for the in-cylinder pressure can be decreased to
a degree where the desired component can be extracted. Moreover, by
using the first and second correlation coefficients, the volume
change rate and the in-cylinder pressure at the desired component
can be more exactly extracted and the time period for which the
engine work is calculated can be arbitrarily established.
Furthermore, according to this invention, because the desired
component suitable for a given engine can be determined, the engine
work of an engine having any structure can be calculated.
According to one embodiment of the invention, the first correlation
coefficient is a Fourier coefficient that is obtained by expanding
the volume change rate into Fourier series. The second correlation
coefficient is a Fourier coefficient that is obtained by expanding
the in-cylinder pressure into Fourier series.
According to one embodiment of the invention, a stroke volume of
the engine is determined. The engine work is calculated based on
the stroke volume, and the first and second correlation
coefficients. Thus, the engine work can be more accurately
calculated even for an engine whose stroke volume is variable.
According to one embodiment of the invention, an operating
condition of the engine is detected. The desired component is
determined based on the detected operating condition. Thus, a
component desired for calculating the engine work can be
appropriately determined in accordance with the operating condition
of the engine.
According to one embodiment of the invention, the desired component
and the first correlation coefficient are predetermined and stored
in a storage device corresponding to the operating condition of the
engine. By referring to the storage device based on a detected
operating condition of the engine, the desired component and the
first correlation coefficient corresponding to the detected
operating condition of the engine are extracted. Thus, the
calculation load for calculating the engine work can be reduced by
predetermining and storing the desired component and the first
correlation coefficient. Furthermore, the stroke volume may be
predetermined and stored in the storage device corresponding to the
operating condition of the engine.
According to one embodiment of the invention, an in-cylinder
pressure of the engine is detected. The second correlation
coefficient is calculated based on the detected in-cylinder
pressure in accordance with a predetermined equation. Thus, the
second correlation coefficient is calculated in real time.
According to one embodiment of the invention, the desired component
can be determined in accordance with a compression ratio of the
engine. Further, the stroke volume and the first correlation
coefficient can be determined in accordance with the compression
ratio of the engine.
In an engine whose compression ratio is variable, a waveform of the
volume change rate may change. By determining the desired
component, the stroke volume and the first correlation coefficient
in accordance with the compression ratio, the engine work can be
more accurately calculated even for an engine whose compression
ratio is variable.
According to one embodiment of the invention, a first component in
a first condition of the engine and a first correlation coefficient
corresponding to the first component are stored in a storage
device. A second component in a second condition of the engine and
a first correlation coefficient corresponding to the second
component are also stored in the storage device. If a detected
operating condition of the engine is between the first condition
and the second condition, a first correlation coefficient
corresponding to the detected operating condition of the engine is
calculated by interpolating between the first correlation
coefficient corresponding to the first component and the first
correlation coefficient corresponding to the second component. Such
interpolation can reduce the number of the desired components and
the first correlation coefficients that are to be stored in the
storage device. Such interpolation can be applied to the stroke
volume.
According to one embodiment of the invention, a volume change rate
corresponding to a detected operating condition of the engine is
determined. The first correlation coefficient is calculated based
on the volume change rate in accordance with a predetermined
equation. Thus, the first correlation coefficient can be calculated
in real time.
The engine work includes an indicated mean effective pressure.
According to another aspect of the present invention, an apparatus
for implementing the above-described method is provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[FIG. 1] A diagram schematically showing an engine and its control
unit in accordance with one embodiment of the present
invention.
[FIG. 2] A diagram showing an indicated mean effective pressure in
accordance with one embodiment of the present invention.
[FIG. 3] A diagram showing a volume change rate in accordance with
one embodiment of the present invention.
[FIG. 4] A diagram showing a result of an FFT analysis on a volume
change rate in accordance with one embodiment of the present
invention.
[FIG. 5] A diagram showing a value of each order Fourier
coefficient in accordance with one embodiment of the present
invention.
[FIG. 6] A diagram showing a volume change rate and values of
Fourier coefficients thereof in accordance with one embodiment of
the present invention.
[FIG. 7] A diagram showing a volume change rate and values of
Fourier coefficients thereof in accordance with one embodiment of
the present invention.
[FIG. 8] A diagram showing a volume change rate and values of
Fourier coefficients thereof in accordance with one embodiment of
the present invention.
[FIG. 9] A diagram showing a volume change rate and values of
Fourier coefficients thereof in accordance with one embodiment of
the present invention.
[FIG. 10] A block diagram of an apparatus for calculating an
indicated mean effective pressure in accordance with one embodiment
of the present invention.
[FIG. 11] A map defining values of a stroke volume and Fourier
coefficients corresponding to a compression ratio in accordance
with one embodiment of the present invention.
[FIG. 12] A flowchart of a process for calculating an indicated
mean effective pressure in accordance with one embodiment of the
present invention.
[FIG. 13] A diagram showing how to establish a calculation interval
in accordance with one embodiment of the present invention.
EXPLANATIONS OF LETTERS OR NUMERALS
TABLE-US-00001 1 ECU 2 Engine 15 In-cylinder pressure sensor 26
Variable compression ratio mechanism 27 Compression ratio
sensor
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments will be now described referring to the
drawings. FIG. 1 shows an overall structure of an engine and its
control unit in accordance with one embodiment of the present
invention.
An electronic control unit (hereinafter referred to as an ECU) 1 is
essentially a computer having a central processing unit (CPU) 1b.
The ECU1 comprises a memory 1c that includes a read only memory
(ROM) for storing programs for controlling each part of the vehicle
and maps required for executing the programs and a random access
memory (RAM) for providing work areas for operations by the CPU 1b
and temporarily storing programs and data. The ECU 1 further
comprises an input interface 1a for receiving data sent from each
part of the vehicle and an output interface 1d for sending a
control signal to each part of the vehicle.
An engine 2 is a 4-cycle engine in this embodiment. The engine 2 is
connected to an air intake manifold 4 through an air intake valve 3
and connected to an exhaust manifold 6 through an exhaust valve 5.
A fuel injection valve 7 for injecting fuel in accordance with a
control signal from the ECU 1 is disposed in the intake manifold
4.
The engine 2 takes air-fuel mixture from air taken from the intake
manifold 4 and fuel injected by the fuel injection valve 7 into the
combustion chamber 8. A spark plug 9 is provided in the combustion
chamber 8 to ignite a spark in accordance with an ignition timing
signal from the ECU 1. The air-fuel mixture is combusted by the
spark ignited by the spark plug 9. The combustion increases the
volume of the mixture, which pushes the piston 10 downward. The
reciprocating motion of the piston 10 is converted into the
rotation motion of the crankshaft 11.
An in-cylinder pressure sensor 15 is, for example, a piezo-electric
element sensor. The in-cylinder pressure sensor 15 is embedded in a
portion of the spark plug 9 that contacts the cylinder. The
in-cylinder pressure sensor 15 generates a signal corresponding to
a rate of change in a pressure within the combustion chamber 8
(in-cylinder pressure) and sends it to the ECU 1. The ECU 1
integrates the signal indicating the rate of change in the
in-cylinder pressure to generate a signal P indicating the
in-cylinder pressure.
A crank angle sensor 17 is disposed in the engine 2. The crank
angle sensor 17 outputs a CRK signal and a TDC signal, which are
pulse signals, to the ECU 1 in accordance with the rotation of a
crankshaft 11.
The CRK signal is a pulse signal that is output at every
predetermined crank angle (for example, 30 degrees). The ECU 1
calculates a rotational speed NE of the engine 2 in accordance with
the CRK signal. The TDC signal is also a pulse signal that is
output at a crank angle associated with the TDC position of the
piston 10.
A throttle valve 18 is disposed in an intake manifold 4 of the
engine 2. An opening degree of the throttle valve 18 is controlled
by a control signal from the ECU 1. A throttle valve opening sensor
(.theta.TH) 19, which is connected to the throttle valve 18,
provides the ECU 1 with a signal indicating the opening degree of
the throttle valve 18.
An intake manifold pressure (Pb) sensor 20 is disposed downstream
of the throttle valve 18. The intake manifold pressure Pb detected
by the Pb sensor 20 is sent to the ECU 1.
An airflow meter (AFM) 21 is disposed upstream of the throttle
valve 18. The airflow meter 21 detects the amount of air passing
through the throttle valve 18 and sends it to the ECU 1.
A variable compression ratio mechanism 26 is a mechanism that is
capable of changing a compression ratio within the combustion
chamber in accordance with a control signal from the ECU 1. The
variable compression ratio mechanism 26 can be implemented by any
known technique. For example, a technique has been proposed for
changing a compression ratio according to the operating condition
of the engine by changing the position of the piston using a
hydraulic pressure.
A compression ratio sensor 27 is connected to the ECU 1. The
compression ratio sensor 27 detects a compression ratio Cr of the
combustion chamber and sends it to the ECU 1.
A signal sent to the ECU 1 is passed to the input interface 1a and
is analogue-digital converted. The CPU 1b processes the resulting
digital signal in accordance with a program stored in the memory
1c, and creates a control signal. The output interface 1d sends the
control signal to actuators for the fuel injection valve 7, spark
plug 9, throttle valve 18, and other mechanical components. The CPU
1b can calculate work performed by the engine using digital signals
thus converted in accordance with one or more programs stored in
the memory 1c.
The indicated mean effective pressure is often used as an index
representing work performed by an engine. The mean effective
pressure is a value obtained by dividing engine work achieved
during one combustion cycle by a stroke volume. The indicated mean
effective pressure is a value obtained by subtracting from the mean
effective pressure, for example, cooling loss, incomplete
combustion, and mechanical friction. These indexes may be used to
evaluate performance gaps among engines having different total
stroke volumes (different engine displacements).
FIG. 2 shows a so-called PV chart that indicates a relationship
between a volume V and an in-cylinder pressure P of the combustion
chamber over one combustion cycle. At P point, the intake valve
opens and the intake stroke starts. The in-cylinder pressure
continues to decrease until the piston reaches U point, which
indicates the minimum value, through N point that is the top dead
center (TDC). Thereafter, the piston passes through K point that is
the bottom dead center (BDC) and the in-cylinder pressure
increases. At Q point, the compression stroke starts and the
in-cylinder pressure continues to increase. At R point, the
combustion stroke starts. The in-cylinder pressure rapidly
increases due to the combustion of the air-fuel mixture. At S
point, the in-cylinder pressure reaches the maximum value. The
piston is pushed down by the combustion of the air-fuel mixture and
moves toward a BDC indicated by M point. This movement reduces the
in-cylinder pressure. At T point, the exhaust valve opens and the
exhaust stroke starts. During the exhaust stroke, the in-cylinder
pressure further decreases.
The indicated mean effective pressure is calculated by dividing the
area surrounded by the curve illustrated in FIG. 2 by the stroke
volume of the piston.
In the following embodiments, a technique for calculating the
indicated mean effective pressure will be described. It should be
noted that the term "engine work" includes other indexes such as
mean effective pressure, brake mean effective pressure, engine
torque or the like which can be derived based on the indicated mean
effective pressure determined by a technique according to the
present invention.
The indicated mean effective pressure Pmi can be calculated by
contour-integrating the PV curve as shown in FIG. 2. This
calculation can be expressed as in the equation (1). An integral
interval corresponds to one combustion cycle. It should be noted
that the starting point of the integral interval can be set at an
arbitrary time point.
The equation (2) is a discrete representation of the equation (1).
Here, m in the equation (2) indicates a calculation cycle. Vs
indicates a stroke volume of one cylinder. dV indicates a volume
change rate of the cylinder. P indicates an in-cylinder pressure
signal that can be determined based on the output of the
in-cylinder pressure sensor 15 (FIG. 1) as described above.
.times. .times.d.times..times..times. ##EQU00001##
As shown by the equation (1), the indicated mean effective pressure
Pmi is represented as a correlation coefficient between the
in-cylinder pressure signal P and the volume change rate dV.
Frequency components substantially constituting the volume change
rate dV are limited (details will be described later). Thus, the
indicated mean effective pressure Pmi can be determined by
calculating the correlation coefficient between P and dV for only
the frequency components constituting the volume change rate.
In order to frequency-resolve the volume change rate dV, the volume
change rate dV is expanded in a Fourier-series, as shown by the
equation (3). Here, t indicates time. T indicates the length of a
rotation cycle of the crankshaft of the engine (referred to as a
crank cycle hereinafter) and .omega. indicates the angular
frequency. As to a 4-cycle engine, one cycle T corresponds to 360
degrees. k indicates the order of the engine rotation
frequency.
.function..omega..times..times..function..times..times..infin..times..ti-
mes..times..times..times..times..omega..times..times..times..times..times.-
.times..times..omega..times..times..times..times..times..times..times..int-
g..times..function..times.d.times..times..times..intg..times..function..ti-
mes..times..times..times..times..omega..times..times..times.d.times..times-
..times..intg..times..function..times..times..times..times..times..omega..-
times..times..times.d ##EQU00002##
The equation (4) is derived by applying the equation (3) to the
equation (1). Here, .theta.=.omega.t.
.times..times. .times.d.times..times.
.times..times..times..infin..times..times..times..times..times..times..th-
eta..times..times..times..times..times..theta..times.d.theta..times..times-
.
.times..times..times..times..times..times..times..times..theta..times..t-
imes..times..times..times..times..theta..times..times..times..times..times-
..times..times..theta..times..times..times..times..times..times..theta..ti-
mes..times..times..times..times..theta..times..times..times..times..times.-
.times..theta..times..times..times..times..theta..times..times..times..tim-
es..times..times..times..theta..times..times.d.theta..times..times.
.times..times..times..times..times.d.theta..times..times..times.
.times..times..times..times..theta..times.d.theta..times..times..times.
.times..times..times..times..times..theta..times.d.theta..times..times..t-
imes..times.
.times..times..times..times..theta..times.d.theta..times..times..times.
.times..times..times..times..times..theta..times.d.theta.
##EQU00003##
On the other hand, the in-cylinder pressure signal P is expanded
into a Fourier series. The Fourier coefficients Pak and Pbk for the
in-cylinder pressure signal can be expressed as shown by the
equation (5). One cycle Tc of the in-cylinder pressure signal has a
length equivalent to the length of one combustion cycle. As to a
4-cycle engine, the cycle Tc is twice the crank cycle T because one
combustion cycle corresponds to 720 degrees crank angle. Therefore,
.theta.c in the equation (5) is .theta./2 in the 4-cycle engine. kc
indicates the order of the in-cylinder pressure signal's
frequency.
.times.
.times..times..times..times..times..times..theta..times..times..t-
imes..times..times..times..theta..times..times.
.times..times..times..times..times..times..theta..times.d.theta..times..t-
imes..times.
.times..times..times..times..times..times..theta..times..times..times..ti-
mes.d.theta..times..times.
.times..times..times..times..times..times..theta..times.d.theta.
##EQU00004##
There are components of cos .theta., cos 2.theta., sin .theta., sin
2.theta., . . . in the equation (4). By assuming kc=2k in the
equation (5), the Fourier coefficients Pak and Pbk for these
components can be determined. That is, in order to calculate the
indicated mean effective pressure Pmi for the 4-cycle engine, only
the second, fourth, sixth, . . . order (kc=2, 4, 6, . . . )
frequency components are required for the Fourier coefficients Pak
and Pbk of the in-cylinder pressure signal, among the first,
second, third, . . . order (k=1, 2, 3, . . . ) frequency components
for the Fourier coefficients Vak and Vbk of the volume change rate.
Assuming kc=2k, the equation (5) can be expressed by the equation
(6).
.times..times.
.times..times..times..times..times..times..theta..times.d.theta..times..t-
imes.
.times..times..times..times..times..times..theta..times.d.theta..tim-
es..times..times..times.
.times..times..times..times..times..times..theta..times.d.theta..times..t-
imes.
.times..times..times..times..times..times..theta..times.d.theta.
##EQU00005##
By applying the equation (6) to the equation (4), the equation (7)
is derived. Here, "Va0" in the equation (4) is almost zero (This
reason will be described later).
.times..times..times..infin..times..times..infin..times..times.
##EQU00006##
The equation (7) includes the stroke volume Vs and the Fourier
coefficients Vak and Vbk for the volume change rate dV. Therefore,
even for an engine in which the stroke volume Vs and the waveform
of the volume change rate dV with respect to the crank angle are
variable, the indicated mean effective pressure Pmi can be more
accurately calculated.
The equation (7) is for a 4-cycle engine. It would be obvious to
those skilled in the art that the indicated mean effective pressure
for a 2-cycle engine can be calculated in a similar way to the
4-cycle engine as described above. In the case of a 2-cycle engine,
Tc=T and .theta.c=.theta..
The equation (6) for calculating the Fourier coefficients Pak and
Pbk of the in-cylinder pressure is expressed in the continuous time
system. The equation (6) is transformed into the discrete time
system appropriate for digital processing, which is shown by the
equation (8). Here, N indicates the number of times of sampling in
each crank cycle T. The integral interval has a length equivalent
to one combustion cycle. The number of times of sampling in each
combustion cycle is 2N. n indicates a sampling number. Pn indicates
an in-cylinder pressure in the n-th sampling.
.times..times.
.times..times..times..times..times..times..theta..times.d.theta..times..t-
imes.
.times..times..times..times..times..times..omega..times..times..time-
s.d.times..times.
.times..times..times..times..times..times..times..pi..times..times.d.time-
s..times..times..times..times..times..times..times..times..times..pi..time-
s..times..times..times..times.
.times..times..times..times..times..times..theta..times.d.theta..times.
.times..times..times..times..times..times..omega..times..times..times.d.t-
imes..times.
.times..times..times..times..times..times..times..pi..times..times.d.time-
s..times..times..times..times..times..times..times..times..times..pi..time-
s. ##EQU00007##
By combining the equations (7) and (8), the equation (9) is
obtained.
.times..times..times..infin..times..times..infin..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.pi..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..pi..times. ##EQU00008##
In this embodiment, as shown by the equation (9), the Fourier
coefficients Pak and Pbk of the in-cylinder pressure are calculated
in real time in response to the detected in-cylinder pressure
sample Pn. The stroke volume Vs and the Fourier coefficients Vak
and Vbk of the volume change rate are pre-calculated and stored in
the memory 1c of the ECU 1 (FIG. 1).
The stroke volume Vs and the waveform of the volume change rate dV
corresponding to the operating condition of the engine depend on
the engine characteristics. Therefore, the stroke volume Vs and the
volume change rate dV corresponding to the operating condition of
the engine can be determined in advance through simulations or the
like. In this embodiment, the stroke volume Vs and the Fourier
coefficients Vak and Vbk corresponding to the operating condition
of the engine are pre-stored in the memory 1c.
Alternatively, the Fourier coefficients Vak and Vbk may be
calculated in real time in response to detecting the volume change
rate. The equation (10) is for this calculation. Here, the integral
interval is one crank cycle T. Vn indicates a volume change rate
acquired in the n-th sampling, into which the detected volume
change rate is substituted.
.times.
.times..times..times..times..times..times..times..pi..times..time-
s.d.times..times..times..times..times..times..times..times..pi..times..tim-
es..times..times.
.times..times..times..times..times..times..times..pi..times..times.d.time-
s..times..times..times..times..times..times..times..pi..times.
##EQU00009##
The integral interval may have a length of 2 crank cycles that is
equivalent to one combustion cycle. In this case, the equation (11)
is used to calculate the Fourier coefficients of the volume change
rate. The calculation result is the same as the equation (10).
.times..times.
.times..times..times..times..times..times..times..pi..times..times.d.time-
s..times..times..times..times..times..times..times..times..times..pi..time-
s..times..times..times..times.
.times..times..times..times..times..times..times..pi..times..times.d.time-
s..times..times..times..times..times..times..times..times..times..pi..time-
s. ##EQU00010##
Now, the Fourier coefficient is considered in detail. As seen from
the equation (8), each of the Fourier coefficients of the
in-cylinder pressure can be considered as a correlation coefficient
between the in-cylinder pressure signal P and a signal that
consists of one of the frequency components obtained by
frequency-resolving the volume change rate dV. Similarly, as seen
from the equation (10), each of the Fourier coefficients of the
volume change rate can be considered as a correlation coefficient
between the volume change rate signal dV and a signal that consists
of one of the frequency components obtained by frequency-resolving
the volume change rate dV. For example, the Fourier coefficient Pa1
is a correlation coefficient between the in-cylinder pressure
signal P and cos .theta.. The volume change rate Vb2 is a
correlation coefficient between the volume change rate signal dV
and sin 2.theta..
Thus, each of the Fourier coefficients of the in-cylinder pressure
indicates an in-cylinder pressure signal extracted at the
corresponding frequency component. Each of the Fourier coefficients
of the volume change rate indicates a volume change rate signal
extracted at the corresponding frequency component. As described
above, because the frequency component(s) substantially
constituting the volume change rate dV are limited, the indicated
mean effective pressure Pmi can be calculated by using the
in-cylinder pressure signal and the volume change rate signal that
are extracted only at such limited frequency component(s). The
present invention provides such calculation technique.
In this embodiment, the Fourier series expansion is used to extract
the in-cylinder pressure signal and the volume change rate signal
at frequency components substantially constituting the volume
change rate. However, this extraction may be implemented by using
another technique.
Now, the equation (9) for calculating the indicated mean effective
pressure Pmi will be discussed referring to various
embodiments.
FIG. 3 shows a waveform 51 of the volume change rate dV and a
waveform 52 of a sine function having the same cycle as the volume
change rate dV for a general engine in which the waveform of the
volume change rate dV with respect to the crank angle is constant
(in other words, the stroke volume is constant and hence there is
no variation in the behavior of the volume change rate dV). The
amplitude depends on the magnitude of the stroke volume. In this
example, the calculation interval A for the Fourier coefficient is
one combustion cycle starting from the TDC (top dead center) of the
intake stroke. The sine function is established to have zero at the
start of the calculation interval A.
As seen from the figure, both waveforms are very similar to each
other, which indicates that the volume change rate dV can be
expressed by a sine function. The volume change rate dV has almost
no offset or phase difference with respect to the sine function.
Therefore, it is predicted that almost no direct current (DC)
component and almost no cosine components appear in the frequency
components of the volume change rate.
FIG. 4 shows a result of an FFT analysis on the volume change rate
dV of such an engine. Reference numeral 53 is a line indicating the
first order frequency of the engine rotation and reference numeral
54 is a line indicating the second order frequency of the engine
rotation. As seen from the analysis result, the volume change rate
dV mainly has only the first and second order frequency components
of the engine rotation.
FIG. 5(a) shows an example of the Fourier coefficients of the
volume change rate dV that were actually calculated for the
calculation interval A shown in FIG. 3. FIG. 5(b) graphically shows
the magnitude of each Fourier coefficient in FIG. 5(a). It is seen
that the direct current component Va0 and the cosine components Vak
(k=1, 2, . . . ) whose phase is shifted from the sine components
are almost zero. It is also seen that the third and higher order
harmonic frequency components (k.gtoreq.3) are almost zero.
Thus, in an engine in which the waveform of the volume change rate
does not change, the volume change rate dV mainly consists of sine
components at the first and second order frequency components of
the engine rotation. In other words, among the Fourier coefficients
of the volume change rate dV, components other than the first and
second order sine components can be ignored. Considering this, the
equation (9) can be expressed as shown by the equation (12).
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..pi..times. ##EQU00011##
In this example, because the stroke volume Vs in the equation (12)
has a constant value, (2N/2Vs) can be handled as a predetermined
value.
Thus, for an engine in which the waveform of the volume change rate
does not change, because the frequency components substantially
constituting the volume change are the first and second sine
components, only the Fourier coefficients Vb1 and Vb2 of the volume
change rate dV and the Fourier coefficients Pb1 and Pb2 of the
in-cylinder pressure P are required for calculating the indicated
mean effective pressure Pmi.
Some variable compression ratio mechanisms change the stroke volume
depending on the operating condition of an engine and hence change
the waveform of the volume change rate dV with respect to the crank
angle. The following embodiments where the variable compression
ratio mechanism 26 shown in FIG. 1 has such characteristics will be
described.
FIG. 6(a) shows a waveform 61 (solid line) of the volume change
rate dV under a certain operating condition as an example. A
waveform 62 of a sine function having the same cycle as the
waveform 61 of the volume change rate dV is also shown. A
calculation interval A is set similarly to FIG. 5 and the sine
function is established to have a value of zero at the start of the
calculation interval A.
The waveform 61 of the volume change rate dV is distorted as
compared with the waveform 62 of the sine function. Therefore, it
is predicted that the volume change rate dV includes not only sine
components but also cosine components. FIG. 6(b) shows values of
the Fourier coefficients for the components of the volume change
rate dV shown in FIG. 6(a), which were actually calculated for the
calculation interval A. It is seen that the volume change rate dV
can be expressed by the first and second order sine components and
the first and second order cosine components. Therefore, the
indicated mean effective pressure Pmi can be expressed as shown by
the equation (13).
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..pi..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..pi..times.
##EQU00012##
A value corresponding to the detected operating condition of the
engine is substituted into the stroke volume Vs in the equation
(13).
Thus, because the frequency components substantially constituting
the volume change rate under this operating condition are the first
and second order sine components and the first and second order
cosine components, only the Fourier coefficients Va1, Va2, Vb1 and
Vb2 of the volume change rate dV and the Fourier coefficients Pa1,
Pa2, Pb1 and Pb2 of the in-cylinder pressure P are required for
calculating the indicated mean effective pressure Pmi.
FIG. 7(a) shows a waveform 71 (solid line) of the volume change
rate dV under another operating condition of the engine. A waveform
72 of a sine function having the same cycle as the waveform 71 of
the volume change rate dV is also shown. A calculation interval A
is set similarly to FIG. 5 and the sine function is established to
have a value of zero at the start of the calculation interval A. It
is seen that the waveform 71 of the volume change rate dV is almost
the same as the waveform 72 of the sine function. FIG. 7(b) shows
values of the Fourier coefficients for the components of the volume
change rate dV shown in FIG. 7(a), which were actually calculated
for the calculation interval A. As seen from the figure, the volume
change rate dV can be expressed only by the first order sine
component.
Thus, because the frequency component substantially constituting
the volume change rate under this operating condition is the first
order sine component, the indicated mean effective pressure Pmi can
be expressed as shown by the equation (14). A value corresponding
to the detected operating condition of the engine is substituted
into the stroke volume Vs in the equation (14).
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..pi..ti-
mes. ##EQU00013##
Considering vibration and friction of the piston movement, it may
be preferable to bring the waveform of the volume change rate dV
close to the waveform of the sine function, as much as possible.
For this reason, an engine may be structured such that the waveform
of the volume change rate dV is similar to the waveform of the sine
function. As shown in FIG. 7, when the waveform of the volume
change rate dV is similar to the sine waveform, the number of
Fourier coefficients required for calculating the indicated mean
effective pressure can be reduced.
Thus, according to the present invention, the Fourier coefficients
of the volume change rate and the in-cylinder pressure do not need
to be calculated for all of the components (namely, for all order
sine/cosine components). It is sufficient to calculate the Fourier
coefficients only for desired components, that is, preferably only
for components required for calculating the indicated mean
effective pressure with a desired accuracy. In the example of FIG.
3, only the Fourier coefficients Vb1 and Vb2 for the first and
second order sine components of the volume change rate dV and the
Fourier coefficients Pb1 and Pb2 for the first and second order
sine components of the in-cylinder pressure P need to be
determined. In the example of FIG. 6, only the Fourier coefficients
Vb1, Vb2, Va1 and Va2 for the first and second order sine and
cosine components of the volume change rate dV and the Fourier
coefficients Pb1, Pb2, Pa1 and Pa2 for the first and second order
sine and cosine components of the in-cylinder pressure P need to be
determined. Thus, by determining only the desired components, the
number of the Fourier coefficients to be calculated can be reduced,
thereby reducing the calculation load for the indicated mean
effective pressure.
A sample Pn of the in-cylinder pressure as shown in the equation
(9) is used to calculate the Fourier coefficients Pak and Pbk in
real time. The sample Pn of the in-cylinder pressure is obtained by
sampling, in a predetermined cycle, the in-cylinder pressure
derived from the output of the in-cylinder pressure sensor.
According to a technique of the present invention, if components
required for calculating the indicated mean effective pressure are
determined, the sampling frequency of the in-cylinder pressure P
can be reduced (down-sampled or decimated) to a frequency that
satisfies the sampling theorem. For example, according to the
equations (12) and (13), the sampling frequency required for
acquiring a sample Pn of the in-cylinder pressure does not need to
be higher than a frequency level required for extracting the first
and second order frequency components of the engine rotation. A
higher sampling frequency for extracting the third and higher
harmonic frequency components of the engine rotation is not
required. Therefore, the sampling frequency can be reduced.
Furthermore, even when aliasing may appear in frequency components
other than the desired components, there is no influence on the
calculation of the indicated mean effective pressure. Therefore,
limitations on an anti-aliasing filter, which may be usually
applied to the in-cylinder pressure signal, can be reduced.
When the Fourier coefficients of the volume change rate are
determined in real time in accordance with the equation (10) or
(11), the sampling frequency of the volume change rate can be also
reduced similarly to the in-cylinder pressure.
Components desired for calculating the indicated mean effective
pressure can be pre-determined through a simulation or the like. In
one embodiment of the present invention, the Fourier coefficients
Vak and Vbk for the desired components and the stroke volume Vs
corresponding to the operating condition of the engine are
pre-stored in the memory 1c (FIG. 1). For example, in an engine in
which the waveform of the volume change rate dV does not change,
the stroke volume Vs and the Fourier coefficients Vb1 and Vb2 have
constant values as described above referring to FIG. 3. These
constant values are stored in the memory. In an engine in which the
waveform of the volume change rate dV changes (as described above
referring to FIGS. 6 and 7), the stroke volume Vs and the Fourier
coefficients Vb1, Vb2, Va1 and Va2 that correspond to one operating
condition of the engine are pre-stored in the memory (in the case
of FIG. 6). The stroke volume Vs and the Fourier coefficient Vb1
that correspond to another operating condition of the engine are
pre-stored in the memory (in the case of FIG. 7). In order to
calculate the indicated mean effective pressure, the memory 1c is
referred to extract the Fourier coefficients of the volume change
rate for the desired components and the stroke volume. Thus,
because the indicated mean effective pressure is calculated by
using the values pre-calculated for the Fourier coefficients of the
volume change rate and the stroke volume, the calculation load for
the indicated mean effective pressure can be reduced.
FIG. 8 shows yet another embodiment, in which the values of the
Fourier coefficients of the volume change rate change although the
types of components desired for calculating the indicated mean
effective pressure do not change. In FIG. 8, a first operating
condition (a1)/(a2) and a second operating condition (b1)/(b2) of
an engine are shown. (a1) and (b1) show waveforms (solid lines) 81,
83 of the volume change rate dV and a waveform (dotted line) 82 of
the sine function having the same cycle as the volume change rate
dV. (a2) and (b2) show the value of the Fourier coefficient for
each component. Between the first and second conditions, the types
of the desired components for calculating the indicated mean
effective pressure do not change (the first order sine component in
the both conditions), but the value of the Fourier coefficient of
the first order sine component changes. Between the first and
second conditions, the stroke volume Vs also changes.
Such changes are caused by the variable compression ratio
mechanism. In the first condition, the stroke volume is Vs1 and the
value of the Fourier coefficient Vb1 is about 4.3. In the second
condition, the stroke volume is Vs2 and the value of the Fourier
coefficient Vb1 is about 5.1.
For each of the first and second conditions, the values of the
stroke volume and the Fourier coefficient can be pre-stored in the
memory 1c (FIG. 1). Depending on whether the detected engine
condition is the first or the second condition, the corresponding
stroke volume and the Fourier coefficient are extracted from the
memory 1c to calculate the indicated mean effective pressure in
accordance with the equation (9).
When the detected engine condition is between the first and second
conditions, values of the stroke volume Vs and the Fourier
coefficient Vb1 that correspond to the detected engine condition
can be calculated by, for example, interpolating between the values
of the stroke volume Vs and the Fourier coefficient Vb1 shown in
(a2) and the values of the stroke volume Vs and the Fourier
coefficient Vb1 shown in (b2). Such interpolation can reduce the
number of the stroke volumes and the Fourier coefficients to be
stored in the memory.
FIG. 9 shows yet another embodiment in which the types of
components desired for calculating the indicated mean effective
pressure change. In the figure, a first operating condition
(a1)/(a2), a second operating condition (b1)/(b2) and a third
operating condition (c1)/(c2) of an engine are shown. As seen from
(a1), (b1) and (c1), the waveform (solid line) of the volume change
rate dV changes as indicated by reference numerals 91, 93 and 94. A
waveform 92 representing a sine function having the same cycle as
the waveform of the volume change rate dV is also shown. (a2), (b2)
and (c2) show the value of the Fourier coefficient for each
component.
Among the first, second and third conditions, the stroke volume and
the types of the desired components required for calculating the
indicated mean effective pressure change. In the first condition,
the stroke volume is Vs1 and the desired component is the first
order sine component Vb1, the value of which is about 4.3. In the
second condition, the stroke volume is Vs2 and the desired
components are the first order sine component Vb1, the first order
cosine component Va1 and the second order cosine component Va2.
Those values are about 4.3, -0.7 and 0.8, respectively. In the
third condition, the stroke volume is Vs3 and the desired component
is the first order sine component Vb1, the value of which is about
5.1.
Similarly to the example of FIG. 8, for each operating condition,
the values of the stroke volume and the Fourier coefficient(s) can
be pre-stored in the memory 1c (FIG. 1). Depending on whether the
detected engine operating condition is the first, second or third
condition, the corresponding stroke volume and the Fourier
coefficient(s) are extracted from the memory 1c to calculate the
indicated mean effective pressure in accordance with the equation
(9).
When the detected current engine condition is between the first,
second and third conditions, the stroke volume and the Fourier
coefficient(s) can be calculated through interpolation. For
example, when it is detected that the engine is between the first
and second conditions, the values of the stroke volume and the
Fourier coefficients Vb1, Va1, and Va2 that correspond to the
detected engine operating condition can be calculated by
interpolating between the values of the stroke volume Vs1 and the
Fourier coefficients Vb1, Va1 and Va2 shown in (a2) and the values
of the stroke volume Vs2 and the Fourier coefficient Vb1, Va1 and
Va2 shown in (b2). In such interpolation, a value of zero can be
set in the values of the Fourier coefficients Va1 and Va2 in the
first condition. Similarly, for example, when it is detected that
the engine is between the second and third conditions, the values
of the stroke volume and the Fourier coefficients that correspond
to the detected engine operating condition can be calculated by
interpolating between the values of the stroke volume Vs2 and the
Fourier coefficient Va1, Vb1 and Va2 shown in (b2) and the values
of the stroke volume Vs3 and the Fourier coefficient Va1, Vb1 and
Va2 shown in (c2). In such interpolation, a value of zero can be
set in the values of the Fourier coefficients Va1 and Va2 in the
third condition.
FIG. 10 is a block diagram of an apparatus for calculating an
indicated mean effective pressure in accordance with one embodiment
of the present invention. Functional blocks 101-105 can be
implemented in the ECU 1. Typically, these functions are
implemented by one or more computer programs stored in the ECU 1.
Alternatively, these functions may be implemented with hardware,
software, firmware or any combination thereof.
The memory 1c of the ECU 1 stores the stroke volume Vs and the
volume change rate Fourier coefficients Vak and Vbk for desired
components, all of which are pre-calculated corresponding to the
compression ratio of the engine. FIG. 11(a) shows an example map
defining the stroke volume Vs corresponding to the compression
ratio Cr. FIG. 11(b) shows an example map defining the values of
the Fourier coefficients Vak and Vbk for desired components
corresponding to the compression ratio Cr.
An operating condition detecting unit 101 detects a current
compression ratio Cr of the engine based on the output of the
compression ratio sensor 27 (FIG. 1). A parameter extracting unit
102 refers to a map as shown in FIG. 11(b) based on the detected
compression ratio Cr to determine desired components for the
Fourier coefficients of the in-cylinder pressure and the volume
change rate. In this example, only the Fourier coefficients Vb1,
Vb2, Va1 and Va2 are defined in the map. Therefore, it is
determined that the desired components are the first and second
order sine components and the first and second order cosine
components.
In determining the desired components, the parameter extracting
unit 102 extracts, for the determined desired components, the
values of the volume change rate Fourier coefficients Vak and Vbk
corresponding to the detected compression ratio. In this example,
Va1, Va2, Vb1 and Vb2 are extracted.
Alternatively, a map other than the map of FIG. 11(b) may be
prepared for defining the types of the desired components
corresponding to the compression ratio.
If the types of the desired components change in accordance with
the compression ratio, the values of undesired components may be
set to zero in the map. When referring to the map, a component
having a value of zero can be determined as an undesired component.
Alternatively, undesired components may not be defined in the
map.
The parameter extracting unit 102 further refers to a map as shown
in FIG. 11(a) to extract the stroke volume Vs corresponding to the
detected compression ratio Cr.
The operating condition detecting unit 101 further determines an
in-cylinder pressure P based on the output of the in-cylinder
pressure sensor 15 (FIG. 1). A sampling unit 103 samples the
in-cylinder pressure P in a predetermined cycle to acquire each
sample Pn of the in-cylinder pressure. In one example, sampling is
performed at every 30 degrees crank angle. Therefore, 2N in the
equation (9) takes a value of 24, which is derived by 720/30 (one
combustion cycle corresponds to 720 degrees crank angle). As
described above, as long as the sampling theorem is satisfied,
down-sampling can be performed in accordance with the desired
components.
An in-cylinder pressure Fourier coefficient determining unit 104
receives the types of the desired components from the parameter
extracting unit 102 to calculate the Fourier coefficients Pak and
Pbk for the desired components. In this example, the desired
components are the first and second order sine components and the
first and second order cosine components. The unit 104 substitutes
a sample Pn of the in-cylinder pressure into the Pak and Pbk
calculation equations (see the equation (9)) to calculate Pa1, Pa2,
Pb1 and Pb2.
A calculation unit 105 uses the Fourier coefficients Pak, Pbk of
the in-cylinder pressure, the Fourier coefficients Vak, Vbk of the
volume change rate and the stroke volume Vs to calculate the
indicated mean effective pressure Pmi in accordance with the
equation (9).
Alternatively, the parameter extracting unit 102 may refer to maps
as shown in FIGS. 11(a) and 11(b) based on a target compression
ratio. However, because the variable compression ratio mechanism
that is capable of changing the compression ratio may have a delay,
it is preferable that the Fourier coefficients of the volume change
rate be determined based on the actual compression ratio.
In another embodiment, as described above, the Fourier coefficients
Vak and Vbk of the volume change rate are calculated in real time
in accordance with the equation (10) or (11). In this case, the
volume change rate Vn corresponding to the detected compression
ratio Cr is determined. For example, the volume change rate
corresponding to the compression ratio can be pre-calculated and
defined in a map. Such a map is stored in the memory. The map is
referred to based on the detected compression ratio to determine
the volume change rate Vn. Such determined Vn is substituted into
the equation (10) or (11) to calculate the Fourier coefficients Vak
and Vbk.
FIG. 12 is a flowchart of a process for calculating an indicated
mean effective pressure in accordance with one embodiment of the
present invention. This process is typically performed by one or
more programs stored in the memory 1c (FIG. 1). This process is
activated, for example, every time a TDC signal indicating the TDC
in an intake stroke is issued.
In this embodiment, the indicated mean effective pressure is
calculated for one combustion cycle immediately before the process
is activated. During the combustion cycle, the in-cylinder pressure
signal is sampled. As a result, 2N samples Pn of the in-cylinder
pressure are acquired.
In step S1, a map as shown in FIG. 11(a) is referred to based on a
compression ratio Cr detected in the combustion cycle to extract
the stroke volume Vs. In step S2, a map as shown in FIG. 11(b) is
referred to based on the detected compression ratio Cr to determine
the types of the desired components and extract the Fourier
coefficients Vak and Vbk of the volume change rate for the desired
components.
In step S3, 2N samples Pn of the in-cylinder pressure are used to
calculate the in-cylinder pressure Fourier coefficients Pak and Pbk
for the desired components.
In step S4, based on the stroke volume Vs and the Fourier
coefficients Vak and Vbk of the volume change rate extracted in
steps S1 and S2 and the Fourier coefficients Pak and Pbk of the
in-cylinder pressure extracted in step S3, the indicated mean
effective pressure Pmi is calculated in accordance with the
equation (9).
In an alternative embodiment, a reference value Vsref for the
stroke volume Vs is first established. Then, R (=Vs/Vsref), which
is a ratio of the stroke volume Vs to the established reference
value Vsref is calculated corresponding to the compression ratio
Cr. For example, in the example of FIG. 6, the ratio R that is
determined corresponding to the compression ratio Cr can be used to
calculate the indicated mean effective pressure Pmi in accordance
with the equation (15).
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..pi..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..pi..times.
##EQU00014##
In yet another embodiment, a ratio between the Fourier coefficients
of the volume change rate are pre-calculated in order to calculate
the indicated mean effective pressure Pmi. For example, the
equation (16) is derived from the equation (12).
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..function..times..times..tim-
es..pi..times..times..times..times..times..times..pi..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..times..times..pi..times. ##EQU00015##
As an example, assuming that Vb1:Vb2=1:0.2 is known in advance
through the FFT analysis or the like, the equation (16) is
simplified as shown by the equation (17).
.times..times..times..times..times..times..times..times..times..times..t-
imes..times..times..times..times..times..times..times..function..times..ti-
mes..times..pi..times..times..times..times..times..times..times..times..pi-
..times..times..times..times. ##EQU00016##
As seen from the equation (17), W is based on a correlation
coefficient Pv between an in-cylinder pressure sample Pn and a
predetermined sine function (sin(2 .pi./N) n+0.2 sin 2 (2 .pi./N)
n). Because the stroke volume Vs and the Fourier coefficient Vb1
can be pre-determined as described above, the indicated mean
effective pressure Pmi can be calculated by calculating the value
of W. Thus, the indicated mean effective pressure Pmi can be
calculated by calculating a single correlation coefficient Pv every
time a sample Pn of the in-cylinder pressure is acquired.
In the above-described embodiments, the indicated mean effective
pressure is calculated by using the Fourier coefficients of the
in-cylinder pressure and the volume change rate that are calculated
for one combustion cycle starting from the TDC in the intake
stroke. In other words, the calculation interval for the Fourier
coefficients is one combustion cycle starting from the TDC in the
intake stroke. Alternatively, the calculation interval for the
Fourier coefficients can be started at any time point.
Referring to FIG. 13, (a) shows a case where the Fourier
coefficients are calculated for the calculation interval A which is
one combustion cycle starting from the TDC in the intake stroke as
described above. The waveform of the sine function is established
to have a value of zero at the start of the calculation interval.
By setting the calculation interval in this way, the similarity
between the waveform of the volume change rate and the waveform of
the sine function is higher. Therefore, the number of components
desired for calculating the indicated mean effective pressure can
be reduced. In the example of (a), it is predicted that the desired
components may be only sine component(s).
On the other hand, (b) shows a case where the calculation interval
B starts at a time delayed by td from the TDC of the intake stroke.
The calculation interval B has a length equal to one combustion
cycle. Similarly to (a), the sine function is established to have a
value of zero at the start of the calculation interval B. As seen
from the figure, similarity between the waveform of the volume
change rate and the waveform of the sine function is lower than
(a). Accordingly, the number of components desired for calculating
the indicated mean effective pressure is greater than (a). It is
predicted that the desired components are not only sine components
but also cosine components. Thus, the types of the desired
components change. However, even if a calculation interval such as
(b) is established, the indicated mean effective pressure can be
calculated in accordance with the same technique as described above
referring to FIGS. 3 through 7.
The present invention can be applied to a general-purpose internal
combustion engine (such as an outboard motor or the like).
* * * * *